Today's deltas:
- qt6-base-fourier built, installed, validated on ohm. Static-idle
journal shows zero GL_INVALID_VALUE post-relogin; the Qt 6
GL_ALPHA bug is genuinely fixed.
- chrome v4 under KWin still stalls — at ~6s vs ~3s pre-Qt-fix, so
the GL_ALPHA churn was contributing some load but wasn't the
primary cause.
- Clean A/B with weston: same chrome v4 binary, same panfrost,
same V4L2, same hardware → swapping KWin → weston turns the
stall off entirely. Chrome plays through with elevated CPU
(~96 % vs KWin's ~50 % when it isn't stalled) because weston
falls back to LINEAR composite vs KWin's fast-tile path.
- mpv triangulation:
--vo=null --hwdec=v4l2request: clean (decode only)
--vo=drm --hwdec=v4l2request: 0.7 % drops in 19 s (KMS scanout)
--vo=gpu-next --hwdec=v4l2request under KWin: 76 % drops, slideshow
Decode + display hardware path is fully capable. The wall is
specifically KWin's compositor scheduling/presentation pipeline on
this stack — panfrost ES 3.2 + V4L2 stateless NV12 dmabuf clients.
KWIN_PIVOT.md rewritten:
- Phase 4 (qt6 patch, ship, upstream) marked done.
- New Phase 5 (find the KWin culprit): WAYLAND_DEBUG on chrome +
KWin to capture the missing wl_buffer.release / wp_presentation
exchange around the 6 s stall, plus strace-on-kwin and
effects-disable bisection.
- New Phase 6 (fix and ship): kwin-fourier package pattern, ohm
validation, bugs.kde.org filing.
Source-grep collapsed Phase 1+2 onto a single pass. KWin's own GL paths
use GL_R8 correctly (gltexture.cpp:61, shadowitem.cpp:494). The
glTexImage2D(GL_ALPHA) calls observed in the journal originate from
Qt 6:
- qtbase/src/opengl/qopengltextureglyphcache.cpp:111-117 — text glyph
cache upload path. The #else branch (active when qtbase is built
with QT_CONFIG(opengles2)) unconditionally uses GL_ALPHA, with no
runtime check for ES context major version. Correct on ES 2.x;
broken on ES 3.x where GL_ALPHA is no longer a valid glTexImage2D
internalFormat.
- qtbase/src/gui/rhi/qrhigles2.cpp:1373-1378 — Qt-Quick-RHI sibling.
Same logic, gated only on caps.coreProfile, missing the ES≥3 case.
- qtbase/src/opengl/qopengltextureuploader.cpp:253-257 — QImage→GL
upload path; same shape.
KWin runs an ES 3.2 context on Mali-G52 panfrost (RK3566), Qt picks
GL_ALPHA, mesa returns GL_INVALID_VALUE, every dependent draw errors
at level 0, the compositor's frame-callback path stalls. KWin is the
visible victim because it's the compositor, but the bug is in Qt.
KWIN_PIVOT.md rewritten: the patch series and packaging now target
qt6-base-fourier instead of kwin-fourier. Three small hunks (~3 lines
each), runtime-safe via existing caps.gles + caps.ctxMajor / surface
format majorVersion checks. Upstream landing path: bugreports.qt.io
+ Gerrit change against qtbase dev branch.
marfrit